1. Field of the Invention
The present invention relates to small form factor pluggable module (“SFP module”) mounting structures, and more particularly, to a mounting structure for an SFP module which is connected to a connector mounted on a printed wiring board.
2. Description of the Related Art
An SFP module such as an optical transceiver used in high-speed optical communications is inserted into and thus connected to a connector mounted on a printed wiring board for communication circuitry. The printed wiring board is provided with a holder for fixing the SFP module accurately and stably near a region where the connector is mounted. The holder serves to guide the SFP module toward the connector and also to stably fix the SFP module connected to the connector (cf. U.S. Pat. No. 6,655,995 B1).
FIGS. 22A, 22B and 22C illustrate conventional mounting structure and method for mounting an SFP module, wherein FIG. 22A shows a state of a printed wiring board before a holder and an SFP module are mounted thereon, FIG. 22B shows how the holder and the SFP module are mounted on the printed wiring board, and FIG. 22C shows how the SFP module is detached from the holder (i.e., from the connector on the printed wiring board).
As shown in FIG. 22A, before the SFP module is mounted, a solder pad 102 for the surface mounting of the connector and a plurality of through holes 103 for passing respective legs of the holder therethrough are formed in a mounting region of the printed wiring board 101 where the SFP module is to be mounted.
Also, as shown in FIG. 22B, the SFP module 104 has an engaging portion 107 protruding from a lower surface of a front end portion thereof. The engaging portion 107 is adapted to fit in a fitting hole 106 formed near an open end of the holder 105 so that the SFP module 104 may be locked after being inserted into the holder 105. To permit the engagement, an escape hole 108 of a relatively large size is formed in the corresponding position of the printed wiring board 101 to allow the engaging portion 107 to project thereinto.
First, the connector 109 is mounted in position by soldering on the surface of the printed wiring board 101. Then, a lower holder 111, which constitutes a lower part of the holder 105, is attached to the printed wiring board 101 such that the connector 109 is situated inside the lower holder 111. In this case, the legs 112 of the lower holder 111 are press-fitted into the respective through holes 103 of the printed wiring board 101, or after the legs are inserted, the legs are soldered to the printed wiring board 101, thereby fixing the lower holder 111 to the printed wiring board 101. Subsequently, the SFP module 104 is placed inside the lower holder 111 so that a rear end portion thereof may be connected to the connector 109. At this time, the SFP module 104 and the lower holder 111 are locked together by fitting the engaging portion 107 into the fitting hole 106. Then, an upper holder 113, which constitutes an upper part of the holder 105, is combined with the lower holder 111, whereupon the mounting of the SFP module 104 is completed.
To detach the SFP module 104 mounted in this manner, first, the engaging portion 107 which is exposed to the underside of the printed wiring board 101 through the escape hole 108 is unlocked or disengaged from the fitting hole 106.
Then, as indicated by the broken lines in FIG. 22C, the SFP module 104 is pulled frontward from the opening of the holder 105 and is detached from the holder 105.
In the conventional SFP module mounting structure, however, the printed wiring board 101 needs to be additionally provided with the escape hole 108 for receiving the engaging portion 107 as mentioned above, which makes the machining complicated. Also, no wiring can be formed in a region corresponding to the escape hole 108 of the printed wiring board 101, giving rise to the problem that the degree of freedom of wiring is limited.
The engaging portion 107 is located near the lower surface of the SFP module 104, and accordingly, the disengagement of the SFP module 104 from the holder 105 needs to be carried out from the bottom side of the escape hole 108, that is, from the underside of the printed wiring board 101 opposite the component mounting side, making the detachment of the SFP module 104 troublesome.
Further, to permit the SFP module 104 to be detached from/attached to the holder 105 for replacement, a space needs to be provided so that the SFP module 104 can be moved frontward/rearward over a given stroke. Because of the stroke thus required, no components can be mounted in a region indicated by hatching in the figures plus the region corresponding to the escape hole 108, which is disadvantageous from the point of view of high-density mounting. Also, these unused regions place restrictions on the positioning of the SFP module 104 on the printed wiring board 101.
FIGS. 23A and 23B are partly cutaway views of a network interface card on which the SFP module is mounted, wherein FIG. 23A shows the holder and the SFP module mounted at a certain position on the printed wiring board of the network interface card, and FIG. 23B illustrates the problem that arises when the SFP module is detached.
If the holder 105 is situated at an arbitrary position on the printed wiring board 101 of the network interface card 115 as shown in FIG. 23A, it is possible that the minimum required bend radius fails to be allowed for optical fiber cables 116 when the fiber cables 116 are detached from/attached to the SFP module 104.
Specifically, when the optical fiber cables 116 are moved frontward/rearward over a given stroke at the time of detachment/attachment as shown in FIG. 23B, an excessive bending load acts upon the optical fiber cables 116, possibly fracturing the fiber cables 116 or adversely affecting the transmission characteristics of light.